The invention relates to a method of obtaining a high-density module from encapsulated modular electronic components. It also relates to modules made up of electronic components obtained by the method, in particular mass memory modules.
Many electronic components are sold in encapsulated modular form and in particular in the form of molded plastics material packages in which the elements constituting the component are buried and provided with connecting leads that project laterally from the package. This is known in the art. In one standard package, the connecting leads are curved so that a flat part is pressed against a printed circuit on which the package rests. This applies in particular to components encapsulated in TSOP (Thin Small Outline Packages), enabling thin assemblies to be produced at reduced cost compared to the corresponding prior art techniques.
In many technical fields, and in the aerospace field in particular, a significant research effort is devoted to miniaturizing equipment to save bulk, weight and cost. This is also well known in the art.
One example of a solution with this aim is disclosed in the document U.S. Pat. No. 5,885,850, which describes the production of modules each made up of a stack of flat encapsulated component packages buried in a block of resin hardened so that the connecting leads of the component are flush with the surface of the block, on at least one face of the block, and can be interconnected and rendered accessible from outside the block by appropriate connecting means known in the art. This MCM-V (Multiple Chips Module-Vertical) technique provides high-density mass memory modules, for example, by vertically stacking TSOP memory chips of the same kind with the ends of their connecting leads interconnected on the faces intended to constitute the flanks of the modules, which are cubic.
However, the packages which can be used to produce modules by stacking them were initially designed to be mounted individually on printed circuits and are relatively thick, for various reasons associated with the conditions of their fabrication, use and their destination. Their thickness is due, among other things, to the need to obtain a stiffness of the packages enabling them to be manipulated without risk of damaging the components that they contain during operations of mounting them on circuit boards. It is also necessary to eliminate the risk of delamination of the molding material at the bottom of the package, under the layer on which the components are formed, which is usually a layer of silicon.
One object of the invention is therefore to exploit a stacking method like that described in the document U.S. Pat. No. 5,885,850 referred to above to produce modules to enable stacking of a significantly greater number of packages than has been possible until now, with equivalent overall dimensions of the finished module.
The maximum height of a module that can be mounted on a printed circuit forming part of an assembly consisting of printed circuits disposed in parallel, for example in an equipment rack, is limited by the spacing between the parallel printed circuits, which is generally standardized. This is known in the art. An increase in the density of components in the vertical plane, for the same module height, can therefore achieve significant savings in terms of the overall size per card, and even reduce the number of cards needed.
The invention therefore proposes a method of obtaining a high-density module from modular electronic components encapsulated in flat monoblock packages in which the elements constituting the components are buried and from which project laterally conductive connecting leads of said elements, in which method the packages are stacked and buried in an insulative block corresponding to at least one module so that the projecting connecting leads of the stacked packages are flush with a surface of the block, on at least one face of said block on which, as required, are formed conductive tracks interconnecting leads and/or contacts for connecting the leads with connecting means external to the module, said method being characterized in that it includes, before stacking the packages, an operation of modifying the connecting leads of the packages in order to reduce their overall size and an operation of reducing the height of the packages by thinning their respective bases.
One embodiment of the method includes reducing the height of the packages by at least partly eliminating a uniform thickness of the molded material constituting the bottom wall of each package.
One embodiment of the method includes reducing the height of the packages by eliminating from the bottom thereof the material constituting the bottom wall of each package and a limited uniform thickness of the substrate layer for component elements that is parallel to said bottom wall in each package.
In one embodiment of the method the operation of modifying the connecting leads of the packages includes a phase of flattening each lead, preferably in a plane parallel to the planes defined by the bottom and top walls of the package, and a phase of homogeneously shortening the leads.
The invention also provides a module produced in the form of a block in which is buried a stack of flat monoblock modular packages of electronic components in which elements constituting the components are buried and from which project laterally conductive connecting leads of said elements, said leads being flush with the surface of the insulative block constituting the module on at least one face of said block on which, as required, are formed conductive tracks interconnecting leads and/or contacts for connecting the leads with connecting means external to the module, characterized in that it includes a stack formed of packages whose respective heights have been reduced by thinning their respective bases, before stacking, and that have preferably had eliminated from their bottom the material of the bottom wall and a limited thickness of a substrate layer for component elements that is parallel to the bottom and top walls of the package.